This invention relates generally to systems for charge deposition printing and, more particularly, relates to charge deposition printing apparatus capable of printing with selectable print density.
Charge deposition printers convert electronic input signals into a corresponding raster print output, utilizing a charge deposition printer head (also referred to as an imaging module or cartridge) having a spaced array of charge-generating chambers or guns. The printer head is positioned opposite a rotating print drum, and RF drive signals are applied along conduits to the guns to provide a charge-generating field for each gun. Control signals are sequentially applied to actuate those guns necessary to generate a desired latent image charge distribution on the drum. The charge on the drum is used to retain toner for subsequent transfer to a recipient sheet pressed against the rotating drum, thereby providing a desired print output image, corresponding to the input signals, on the recipient sheet.
The imaging module is typically a replaceable element, and the array of charge deposition chambers is controlled by electrodes which are individually driven by clocked driver elements to generate the charge image on the surface of the rotating imaging drum. Charge deposition printing processes and apparatus are disclosed in commonly owned U.S. patent application Ser. No. 07-063,155, incorporated herein by reference. Charge deposition printers are widely utilized, and provide advantages in resolution, throughput and reliability.
Conventional charge deposition printers, however, can generate print output having only a single resolution (also referred to as print density or dot density). Print resolution in the process direction--i.e. the direction of rotation of the imaging drum--is a function of the resolution of position encoding elements, while print density in the direction transverse to the process direction is determined by the group density of the charge deposition chambers in the imaging module. The resolution of the position encoding elements is typically fixed, and group density is a fixed, characteristic density for a given imaging module.
The print industry has long recognized a need for charge deposition printing apparatus capable of printing with selectable resolution or density, without the necessity of extensive electromechanical reconfiguration, and attendant downtime and loss of throughput. Plural host computers, for example, may each support different levels of print resolution or density, and if utilized in conjunction with conventional charge deposition printing apparatus, would necessitate either the expense of two separate printers, or time-consuming reconfiguration of a single dedicated printer. Moreover, various print applications may require differing levels of resolution even within the same document, such as for text and graphics fields.
Accordingly, there exists a need for charge deposition printing apparatus capable of printing with selectable print density without necessitating extensive electromechanical reconfiguration.
It is therefore an object of the invention to provide charge deposition printing apparatus capable of printing with selectable print density or resolution.
It is a further object of the invention to provide such charge deposition printing apparatus capable of attaining multiple print resolution levels without extensive electromechanical reconfiguration.
Other general and specific objects of the invention will in part be obvious and will in part appear hereinafter.